The Western diet is a known driver of disease because it is devoid of adequate nutrients and also contains metabolic poisons. In particular, the Western diet is increasingly being linked to cardiovascular disease, and regular consumption is known to elevate blood pressure. Some evidence suggests that the very high animal protein content of the Western diet may contribute to blood pressure elevations. This viewpoint is controversial, and it must be clear that associations are not the same as cause and effect. For example, the lower blood pressure seen in vegetarians might relate to their higher potassium intake through their increased consumption of fruits and vegetables. However, the amino acid profiles of vegetable and animal proteins are quite different. Animal protein tends to be high in alanine, arginine, aspartic acid, glycine, histidine, lysine, methionine and threonine, whereas vegetable protein tends to be high in cysteine, glutamic acid, phenylalanine, proline and serine. These differing profiles may initiate quite different physiological responses.
Researchers have attempted to assess the associations between dietary amino acids and blood pressure using observational studies. This sort of study involves measuring a number of parameters in free living subjects and trying to find associations between the parameters. In one study1, the dietary intake of amino acids was estimated from a food questionnaire and the blood pressure of subjects were then taken on a number of occasions to assess any possible correlations. As a percentage of total protein intake, dietary glycine was found to be associated with blood pressure. Because of the risk of confounding variables, the authors then re-assessed the association between glycine and blood pressure by controlling for other factors that are known to cause elevations in blood pressure (for example, maybe glycine intake increases with age and age is actually the cause of the elevated blood pressure). However, when they did this for 16 known confounding variables the association between glycine and blood pressure remained.
From the data the authors estimated that for each additional 0.71 grams per day of glycine, there was an increase in systolic blood pressure of 2 to 3 mm Hg. When the authors assessed the origins of the subjects in the study, they found that the association between glycine and blood pressure was higher in Westerners when compared to Asians. This is interesting because while meat in the main form of protein in Western nations, in the Asian populations of the East, vegetable proteins predominate. The same authors had performed similar research previously and found that glutamic acid, an amino acid found in high concentrations in vegetable protein was inversely associated with blood pressure. This supports the current nutritional view that diets high in plant material are beneficial to the health because they have blood pressure lowering effects. As to the question of whether amino acids can actually cause those effects, or are simply markers of a type of diet consumed, the answer is not known. However, no mechanisms exists to explain the ability of individual amino acids in protein to affect blood pressure.